A recording disc of the above type is shown in FIGS. 1 and 2, wherein a recording disc 2, such as magnetic recording disc or optical recording disc, is rotatably enclosed in a hard disc case 1 having a generally rectangular shape. The recording disc 2 is composed of a recording medium 7 made of an annular magnetic or optical recording sheet and a hub 8 secured to the central portion of the recording medium 7 with the hub 8 disposed facing two drive shaft insertion holes 4 defined on both of a top half 1a and a bottom half 1b of the disc case 1. When the recording disc cartridge is mounted on a disc drive apparatus, the hub 8 is clamped by a hub supporting member 12 and a collet 13 each provided on the disc drive apparatus (FIG. 2) so as to come into contact with the top face 8a and the bottom face 8b of the hub 8, passed through the drive shaft insertion holes 4, whereby the recording disc 2 is rotated by rotation of the hub supporting member 12. In a recording disc cartridge of this type, the hub must have a predetermined thickness with an extremely high accuracy. Therefore, the hub is usually made of polyacetal or polyallylate having good moldability and stability in terms of dimension. In manufacturing, in order to assure an integral combination between the hub and the recording medium, the top half and the bottom half of the hub are separatedly molded, then the halves are opposed and combined together to clamp the peripheral portion of the central hole of the recording medium interposed between the two hub halves.
However, the recording disc cartridge of this type is generally expected to be used under a temperature range between 5.degree. C. and 60.degree. C. Under such circumstances, there may occur a problem of deformation of the hub due to the thermal expansion in the case where the hub is made of a plastic resin. The hub 8 is provided with a hole 9 for engagement of a spindle 14 projected from the hub supporting member 12 of the disc drive apparatus. When in use, each recording track on the recording medium traced by a recording head of the ecording/reproducing apparatus is defined by the accuracy of the center of the hole 9 and the center of the spindle 14 when the recording disc 2 is mounted on the disc drive. Therefore, the center of the hole 9 must coincide with the center of the spindle 14 to a high degree of accuracy. If the hub is thermally deformed, there may occur a problem of tracking error. In addition, in a case where the hub is made of a plastic resin material, the smaller the size of the hub, the lower the mechanical strength thereof.
Furthermore, if the recording medium 7 is a magnetic recording sheet having a base film made of a polyester resin with a magnetic layer coating, the magnetic recording sheet may be creased due to the difference in the amount of deformation of the hub and the recording sheet by the difference of the thermal expansion co-efficients between the hub and the magnetic recording sheet.